Iother = combined i nputof all otherthanfan-assisted
Ifan= combined i nputof all fan-assisted a ppliances in
Btuh/hr ACH= airchanges perhour(ACH shall n otexceed
0.60.) Thefollowing r equirements applyto the Standard
Method and totheKnown AirInfiltration Rate Method.
1.Adjoining rooms c anbeconsidered
partofa space if:
a.There arenocloseable doors b etween rooms.
b.Combining spaces o nsame floorlevel. E ach open-
ingshall h ave free area ofatleast 1 in.2/1,000 Btuh
(2,000 m m2/kW) ofthetotal i nput r ating ofallgas
appliances inthespace, butnotlessthan100 in. 2
(0.06 m2). O ne opening shall c ommence within 12
in.(300 mm) o ftheceiling a nd thesecond o pening
shall c ommence
within 12in.(300 mm) o fthefloor.
Theminimum d imension ofairopenings shall b eat
least 3 in.(80mm). ( SeeFigure 8 )
c.Combining space ondifferent floorlevels. The
volumes ofspaces o ndifferent floorlevels s hall b e
spaces i fconnected
byone ormore permanent openings indoors o r
floors having f ree area ofatleast 2 in.2/1,000 Btuh
(4,400 m m2/kW) oftotal i nput r ating ofallgasappli-
2.Anattic orcrawlspace may beconsidered aspace that
withtheoutdoors provided there
areadequate permanent ventilation openings directly
to outdoors h aving freeareaofat least 1 -in.2/4,000
Btuh oftotal i nputrating forallgasappliances inthe
3. Inspaces t hatusetheIndoor C ombustion
infiltration should beadequate to provide a irforcom-
bustion, p ermanent ventilation a nd dilution of flue
gases. However, inbuildings withunusually tightcon-
struction, additional air MUST beprovided u sing the
methods described in theOutdoor C ombustion Air
Unusually tight c onstruction
isdefined a sConstruction
a.Walls a ndceilings e xposed totheoutdoors have a
continuous, sealed v apor b arrier. Openings aregas-
keted orsealed a nd
b. Doors a ndopenable windows areweatherstripped
c.Other o penings arecaulked o rsealed. These in-
clude joints around w indow anddoor f rames,
between sole plates a ndfloors, between wall-ceil-
ing joints, b etween wall p anels, atpenetrations
plumbing, electrical and gaslines, etc.
ofIndoor andOutdoor Air
1.Indoor o penings shallcomply w iththeIndoorCom-
bustion Air Method below and,
2. Outdoor openings shall b elocated a s required i nthe
Outdoor C ombustion A ir Method mentioned previ-
ously a nd,
3. Outdoor openings shall b esized asfollows:
a.Calculate theRatio ofallIndoor Space v olume d i-
vided byrequired volume f orIndoor C ombustion
Air Method below.
b.Outdoor opening sizereduction Factor i s1minus
c.Minimum s izeofOutdoor openings shall b ethesize
required inOutdoor Combustion Air Method
above m ultiplied byreduction Factor i nb.above.
The minimum d imension ofairopenings shall b e
Bottom Return Air Inlet
installed in bottom return-air
opening. Remove and discard
this panel when bottom return air is used. To remove bottom
closure panel, perform the following:
1. Tilt or raise furnace and remove 2 screws holding bot-
tom filler panel. (See Figure 9.)
Figure 9 -- Removing Bottom Closure
2. Rotate bottom filler panel downward to release holding
3. Remove bottom closure panel.
4. Reinstall bottom filler panel and screws.
Side Return Air Inlet
installed in bottom return-air
opening. This panel MUST be in
place when only side return air is used.
openings can be used in UPFLOW
and most HORIZONTAL
Do not use side
openings in DOWNFLOW
In upflow position with side return inlet(s), leveling legs may
be used. (See Figure 10) Install field-supplied,
5/16 x 1-1/2
in. (8 x 38 mm) (max) corrosion-resistant
washers and nuts.
Bottom closure must be used when leveling legs are
used. It may be necessary to remove and reinstall bottom
to install leveling
legs. To remove bottom
closure panel, see Item 1. in Bottom Return Air Inlet section.
441 01 1402 02